The present invention relates to a developer (developing agent) collecting/charging device to be used in electrophotographic image forming apparatuses such as printers, copiers and facsimiles, as well as to an image forming apparatus and a cleaning method using a developer collecting/charging member.
Conventionally, there have been known so-called 4-cycle full-color image forming apparatuses. Such an image forming apparatus includes a developing unit holding four developing devices corresponding to toners of four colors, yellow (Y), magenta (M), cyan (C) and black (K). With this developing unit rotated so that a developing device is moved to a development position facing an image carrier, an electrostatic latent image on the image carrier is developed by a first-color toner fed from the developing device, by which a toner image is formed on the image carrier. Then, the first-color toner image formed on the image carrier is primarily transferred onto a transfer belt as an example of a transfer member.
Upon termination of the toner image formation on the image carrier with the first-color toner, the developing unit is rotated so that a second-color developing device is moved to the development position, and a second-color toner image is formed on the image carrier by the toner fed from this developing device. Then, the second-color toner image is primarily transferred so as to be superimposed on the first-color toner image on the transfer belt.
Such an image formation process is performed also for the third- and fourth-color toners in succession so that the toner images are primarily transferred successively in superimposition on the first- and second-color toner images on the transfer belt.
A toner image composed of four-color toners, which has been formed in the way described above, is secondarily transferred onto a sheet of paper as a recording medium. The sheet on which the toner image has been secondarily transferred passes through a fixing member so as to have the toner image heated and fixed thereon, thereafter being discharged outside the apparatus. Thus, output of a full-color image is completed.
Provided that such a four-cycle image forming apparatus as described above includes a cleaning device which is provided therein so as to be movable into and out of contact with the transfer belt, the cleaning device that has withdrawn at a position away from the transfer belt during an image formation process is moved to a position where the cleaning device comes into contact with the transfer belt after the secondary transfer, by which toner remaining on the transfer belt after the secondary transfer is collected and cleaned by the cleaning device.
However, providing such a cleaning device for the transfer belt as described above would involve an additional need for a contact-and-separation drive mechanism, which would be an obstacle to the attainment of scale-down and cost reduction of the 4-cycle image forming apparatus.
JP H10-49023 A and JP 3733249 A disclose 4-cycle image forming apparatuses in which after-transfer remaining toner remaining on the transfer belt after the secondary transfer is reversely transferred onto the image carrier so as to be collected. In this case, with a view to facilitating the reverse transfer of the after-transfer remaining toner from the transfer belt to the image carrier, a voltage in which an AC voltage is superimposed on a DC voltage is applied to the after-transfer remaining toner by a charging roller so that the after-transfer remaining toner is uniformly charged to a polarity reverse to a normal polarity.
However, since the charging roller described in JP H10-49023 A and JP 3733249 A is located in such close proximity as to make contact with the transfer belt, the transfer belt may come into contact with, and disturb, the four-color toner image that is transferred one after another by four rotations of the transfer belt during the formation of a color image. For avoidance of this, the charging roller inevitably needs to be kept at a position withdrawn away from the transfer belt during the image formation, making it necessary to provide a contact-and-separation drive mechanism for the charging roller.
With the after-transfer remaining toner left in a large quantity, there are some cases where part of the after-transfer remaining toner is not charged to a polarity reverse to a normal polarity even if a voltage in which an AC voltage is superimposed on a DC voltage is applied by the charging roller. As a result, the after-transfer remaining toner that remains at the normal polarity is not reversely transferred to the image carrier, being uncollected, and could adversely affect the following image formation.